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...... Lightening Wrist & Claws ......

The plan is to have fully articulated arms, one of the problems with that is the torque required to lift the wrist and claws. Am using the resin wrist and claws from Bill K, they are very nice but quite heavy, so i decided to lighten them as much as possible.

For the wrist the obvious solution was to remove material from the inside where it wont show. Decided to "skin" the claws - an idea copied from the styrene R2D2 builders - they build a framework, then wrap a "skin" of thin styrene sheet around it, and glue it in place. Only difference is the framework would be made by hollowing out the claws with a drill/Dremel.

Took out most wrist material with the lathe at the Sydney Robot Workshop, then finished off with the Dremell.

The bulky scissor action will be replaced with 2 small gears to keep claws acting together, with a servo motor mounted directly on one of the gears.

These small aluminium gears came from a set of robotic pinchers, they were just the right size and about $10 from SparkFun Electronics or ebay.

The "dog-leg" on the end of the claws is not needed either.

Marked out the cut-out region leaving about 3mm wall thickness, and set the drill stop to leave similar clearance at the bottom.

After drilling out most of the volume, tidied up with the Dremell sanding wheel.

Will be using a servo motor directly on one of the claws, so won't need most of this material.

Cut off the slide section for the scissor mechanism.

Trimmed the width of the sides.

Before and After shot of the wrist, i wont be needing those 6 holes for mounting the centre plate so it has all been hollowed out.

Before and After shot of the claws, before adding the "skin".

Before and After shot of the centre plate/bracket, it will have a thin piece of material around the edge to keep it located over the centre.

Some of the parts no longer needed.

Here is a table showing the weights of the parts before and after modifying:

  Before After
Wrist 830g 310g
Plate 175g 69g
Claws x2 320g 170g
Unused screws/links etc 200g 0
Additional bits 0 40g(?)
Total 1,525g 589g


Since then i have purchased the fibreglass wrists from Craig, they are even lighter (260g), yet stronger. Available here:

Go to New Wrist Inserts